Dans ce travail, des écoulements liquide-liquide dispersés homogènes (c'est-à-dire sans gradient de concentration) ont été étudiés dans une conduite horizontale de 7.5m de long et de 50mm de diamètre interne. Les expériences ont été réalisées dans une large gamme de paramètres opératoires (vitesses de mélange comprises entre 0.28 et 1.2m/s et concentration volumique en phase dispersée, f, de 0.08 à 0.7). Le facteur de frottement de ces écoulements a été mesuré et modélisé en régime turbulent, intermédiaire et laminaire. Ces différents régimes ainsi que l’effet de la concentration en phase dispersée ont été identifiés à partir des mesures locales de vitesse par une technique de vélocimétrie par image de particules (PIV). Lorsque f=0.56, les dispersions se comportent comme des fluides newtoniens auxquels le concept de viscosité effective peut s’appliquer. Le modèle de viscosité de Krieger et Dougherty (1959) décrit l’ensemble des émulsions formées. Le facteur de frottement mesuré suit les lois de frottement classiques en régime laminaire et turbulent (Hagen-Poiseuille et Blasius respectivement) en fonction du nombre de Reynolds basé sur les propriétés de mélange des émulsions (densité et viscosité). Toutefois, la concentration en phase dispersée induit un retard à l’apparition de la turbulence. En milieu très concentré (f=0.7), la dispersion a un comportement rhéofluidifiant et suit la loi d’Ostwald avec un exposant, n=0.5. Tous ces écoulements ont été étudiés, en détail, par l’analyse locale des vitesses. / Homogeneous dispersed flows have been investigated in a horizontal pipe (7.5m long and 50mm internal diameter) in a wide range of flow parameters (mixture velocity from 0.28 to 1.2m/s and concentration, f, up to 0.7). In this work, the wall friction of this emulsion has been measured and modeled in turbulent, intermediate and laminar regime. The different flow regime and the effect of dispersed phase volume fraction have been determined from the velocity profiles measured by PIV measurements in a refractive index matched medium. When f=0.56, emulsion behaves as newtonian fluid. It was shown that the concept of effective viscosity is relevant to scale the wall friction of the emulsion flow. The effective viscosity follows the classical trend of low inertia suspension of hard spheres (Krieger & Dougherty 1959). The friction factor is described by the classical single phase laws in turbulent and laminar regime (Hagen-Poiseuille and Blasius respectively) as a function of Reynolds number based on mixture properties (density and viscosity). Compared to single phase flow, the transition to turbulence is delayed as dispersed phase fraction is increased. For higher dispersed phase fraction (f=0.7), emulsion behaves as a shear-thinning fluid. Emulsion follows the Ostwald law with an exponent equal to 0.5. All these homogeneous dispersed flow have been studied in details.

Selective laser melting (SLM), is a type of additive manufacturing, which selectively melts a pre-spread layer of metal powders and produce a part by a layer-on-layer manner. SLM has demonstrated a great potential to reduce size and weight in hydraulic manifolds. However, a theoretical base is lacking since friction loss is unclear in a SLMed fluid passage. In this study, various fluid passages without supports, from diameters from 4 mm to 16 mm, were produced horizontally using SLM. The profile was measured using a 3D scanner and surface roughness was measured using a confocal laser scanning microscope. Friction factor was studied using simulation, experiments, and classical theory. The hydraulic diameter of the SLMed passages is smaller than the design diameter. Surface roughness is extremely high on the top part of the inner wall while the rest part is around 10 μm. Such trends are irrelevant of passage diameters. Friction factors in SLMed passage is much larger than those predicted using Moody theory, particularly in laminar flow. The transition from laminar flow to turbulent flow appears at a smaller Reynolds number with increased passage diameter. The influence of the profile overweighs that of the surface roughness on friction factor.

No description available.

Computational fluid dynamics (CFD) modeling is possibly the best available technique in designing and predicting the performance of Stirling and pulse tube refrigerators (PTR). One of the limitations of CFD modeling of these systems, however, is that it requires closure relations for the micro porous materials housed within their regenerators and heat exchangers. Comprehensive prediction of fluid-solid interaction through this media can be obtained only by direct pore level simulation, a process which is time consuming and impractical for system level examination. Through the application of empirical correlations including the Darcy permeability and Forchheimer's inertial coefficient, the microscopic momentum equations governing fluid behavior within the porous structure can be recast as viable macroscopic governing equations. With these constitutive relationships, CFD can be an efficient and powerful tool for system modeling and optimization. The purpose of this study is to determine the hydrodynamic parameters of two mesh fillers relevant to miniature PTRs; stacked screens of 635 mesh stainless steel and 325 mesh phosphor-bronze wire cloth. Experimental setups were designed and fabricated to measure steady and oscillatory pressures and mass flow rates of the working fluid, research-grade helium. Hydrodynamic parameters for the two mesh fillers were determined for steady-state and steady periodic flow in both the axial and radial directions for a range of flow rates, operating frequencies and charge pressures. The effect of average pressure on the steady axial flow hydrodynamic parameters of other common PTR filler materials was also investigated. The determination of sample hydrodynamic parameters and their subsequent computational and experimental methodologies utilized are explained.

The master thesis deals with the design, tracing and dimensioning of condensate pipeline. In the beginning, a preliminary calculation of heat balance is done. It is followed by a description of the main condensate system supplemented by the computational design of pipeline and the calculation of pressure losses in this pipeline. The crucial part of the thesis is the calculation of pressure losses, which is done in two ways. The first approach to calculation of pressure losses in the pipeline is calculated using values of representative resistance coefficient for pipe ele-ments using Idelchik literature and for individual types of valves using values from datasheets of Siemens Energy suppliers. In the second approach to calculation representative resistance coefficients for pipe elements and individual types of valves CRANE literature are used. Then both approaches of choosing representative resistance coefficients are compared and evaluated. Based on the calculated values, a suitable pump is selected at the end of the master thesis.

The cooling systems in a gas turbine are especially important as the turbine blades and vanes are exposed to extreme temperatures. The relatively cool air is extracted from the compressors and fed to the turbines to cool the turbine blades. The manufacturing of these blades and channels used to cool is especially complicated using conventional manufacturing techniques. Additive Manufacturing (AM) gives the designer much more freedom to design core components. The AM technique currently explored is the Selective Laser Melting process (SLM). The surface area is exposed to the cooling airflow by using lattice structures which can be manufactured at relative ease using AM. This thesis will provide some insights into using AM parts for the cooling, by analyzing the pressure drop that could be expected from superalloys that are manufactured using AM. The surface roughness is an inherent property of the AM components therefore it would be interesting to analyze a turbulent flow through AM channels (CM247LC and INCONEL 939). The thesis deals with turbulent flows as the airflow used for cooling in the gas turbine is most likely turbulent.  The friction factor (Darcy–Weisbach friction factor) is used to relate the impact of the surface roughness to the pressure drop. The results from the previous experiments are contrasted as the flow in the previous experiments was assumed to be fully developed but in reality, it was not. And the accuracy of the previous results to the actual fully developed flow will shed some light on the feasibility of the flow analysis techniques used in the previous experiments. It is found that the previous experimental results for the CM247LC TPs have good agreement with current experimental results but INCONEL 939 exhibits significant deviation. The possible reasons for the deviations are directly linked to the assumptions made to calculate the minor losses. The Test Pieces (TP) analyzed in this thesis have varying length to diameter (L/D) ratios and the impact of the variation of different L/D ratios is analyzed along with varying pressure ratios. Where the flow resistance increases with an increase in L/D and pressure ratio. The technique to accommodate the compressibility of the airflow is also explored in this thesis. Finally, reasons for the manifestation of anomalies are discussed. The probability of the compressibility effects of the airflow on the anomalies was found to be quite high, and concluding remarks are provided.

This bachelor thesis is written for KTH Royal Institute of Technology and Ymer Technology AB. It examines the friction factor associated with the pressure drop in wavy-fin heat exchangers. Previous studies have used a nonlinear approach for determining the regression coefficients. This study introduces a linearizing transform that solves the issues of finding non-optimal parameter values stemming from the current nonlinear approach. The linearization also drastically improves the computational time. A final model explaining 95.4\% of the variance in the data is presented. Methods for avoiding overfitting, detecting outliers and hidden extrapolation are presented and used to evaluate the model. The implications of the mathematical results on improving profit, competitiveness, and customer relationships are analyzed in the second part of the report with a qualitative approach. / Denna kandidatuppsats är skrivet vid Kungliga Tekniska Högskolan och Ymer Technology AB. Det undersöker den friktionsfaktor som associeras med tryckfallet i kylare med wavy-fins. Tidigare studier har använt ett ickelinjärt tillvägagångssätt för att bestämma regressionskoefficienterna. Denna studie introducerar en linjäriserande transform som löser problemen med att hitta icke-optimala paramatervärden, som härstammar från tidigare icke-linjära tillvägagångsätt. Linjäriseringen visar sig även förbättra beräkningstiden drastiskt. En slutgiltig modell som förklarar 95\% av variansen i datan presenteras. Metoder för att undvika overfitting, identifiera outliers, och undvika att falla offer för gömd extrapolation presenteras och används för att evaluera modellen. De matematiska resultatens implikationer för Ymer med avseende på vinst, konkurrenskraft och kundrelationer, analyseras i den andra delen av rapporten med en kvalitativ ansats.

Two computational fluid dynamics models are developed to predict the performance of a solid oxide fuel cell stack, a detailed and a simplified model. In the detailed model, the three dimensional momentum, heat, and species transport equations are coupled with electrochemistry. In the simplified model, the diffusion terms in the transport equations are selectively replaced by rate terms within the core region of the stack. This allows much coarser meshes to be employed at a fraction of the computational cost. Following the mathematical description of the problem, results for single-cell and multi-cell stacks are presented. Comparisons of local current density, temperature, and cell voltage indicate that good agreement is obtained between the detailed and simplified models, verifying the latter as a practical option in stack design. Then, the simplified model is used to determine the effects of utilization on the electrochemical performance and temperature distributions of a 10 cell stack. The results are presented in terms of fluid flow, pressure, species mass fraction, temperature, voltage and current density distributions. The effects of species and flow distributions on electrochemical performance and temperature are then analyzed for a 100 cell stack. The discussion highlights the importance of manifold design on performance and thermal management of large stacks. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-09-30 15:55:18.627

<p> Wire-wrapped rod bundles are often used in nuclear reactors operating in a fast neutron spectrum, as designers seek to minimize neutron scattering by packing the fuel pins into a hexagonal lattice. Bundles with many rods have extensively been studied as representative of large fuel assemblies, however far fewer experiments have investigated bundles with 7 rods (7-pin bundles). The large difference in subchannel number between these bundles leads to 7-pin bundles having different pressure drop characteristics. The Versatile Test Reactor (VTR) sodium cartridge loop proposes to use a 7-pin bundle as its experimental core region, highlighting the need for additional data and models. The current work seeks to establish a better understanding of the pressure drop in 7-pin wire-wrapped rod bundles through scaled experiments and a novel pressure drop model. A scaling analysis is first performed to demonstrate the applicability of water experiments to the VTR sodium cartridge loop, before an experimental test facility is designed and constructed. Experiments are then performed at a range of Reynolds numbers to determine the pressure drop. Current models are able to predict the data well, but are complex and can be difficult to use. A comparatively simpler model is developed, based on exact laminar solutions of a simplified rod bundle, which also offers a theoretical lower bound for the pressure drop in wire-wrapped bundles. The proposed model compares well with the existing experimental database, able to predict bundle friction factor with an average absolute percent difference of 10.8%. This accuracy is also similar to existing correlations, while relying on fewer empirical coefficients. The theoretical lower bound is also used to identify several datasets in literature that may feature data that is systemically lower than the true pressure drop, which agrees with previous observations in literature. </p>